1. Field of the Invention
The present invention relates generally to flip-chip semiconductor devices and, more specifically, the present invention relates to improved heat dissipation in flip-chip semiconductor devices.
2. State of the Art
Semiconductor devices inherently generate heat during operation which must be dissipated to maintain the semiconductor device at an acceptable operating temperature. As the operating speed of a semiconductor device increases, typically, the semiconductor device has increased power dissipation and increased heat generated. For example, high operating speed microprocessors tend to have higher power requirements and to generate more heat at the higher operating speeds.
Additional heat dissipation issues arise in the case where the semiconductor device is configured as a xe2x80x9cflip-chip.xe2x80x9d In flip-chip configuration, the surface of a semiconductor die which has an electronic device formed therein directly opposes a die-attach substrate. The semiconductor die is typically attached to the die-attach substrate only by conductive bumps which lead to the bonding pads of the semiconductor die. Typically, electrical traces printed on the die-attach substrate lead from the bumps to provide interconnection to other circuit components.
The described flip-chip configuration gives rise to heat dissipation problems because most of the heat generated by a semiconductor device is generated at the active surface of the semiconductor die. In the flip-chip configuration, the active surface of the semiconductor die is sandwiched against a die-attach substrate which is typically a ceramic insulator, a relatively poor heat-sink, having the space between the semiconductor die and the substrate filled with an underfill material to increase the strength of the connection between the semiconductor die and the substrate as well as to help prevent environmental attack of the electrical circuitry and connections to the substrate. As a result, the majority of the heat generated by a flip-chip semiconductor die is not efficiently dissipated. As such, the conductive bumps provide an extremely small surface area through which the heat must be dissipated, resulting in undesirable localized xe2x80x9chot points or hot spots,xe2x80x9d which often result in thermal fatigue in the interconnections of the conductive bumps.
In an effort to prevent such localized hot points, U.S. Pat. No. 5,508,230 to Anderson et al. discloses a flip-chip assembly having improved heat dissipating capability. As shown in drawing FIGS. 1(a) and 1(b), the flip-chip semiconductor device assembly in the ""230 Patent includes a diamond layer 16 over the active surface 14 of the semiconductor die 10 and a metalized pad 20 provided in a center portion over the top of the diamond layer 16. The solder bumps 22 are provided through openings 18 in the diamond layer 16. A die attach substrate 12 is connected to the semiconductor die 10 so that the solder bumps 22 and the metalized pad 20 are directly contacting the die attach substrate 12. In this manner, heat is dissipated across the diamond layer 16 and is drawn off the device into the metalized pad 20. Although the diamond layer 16 is an excellent conductor of heat, the heat may become trapped in the metalized pad 20, resulting in thermal fatigue between the semiconductor die 10 and substrate 12 since the metalized pad 20 abuts with the substrate 12. Furthermore, the diamond layer 16 includes openings 18 for the solder bumps 22 to protrude therethrough, in which the solder bumps 22 have little, if any, contact with the diamond layer 16. This lack of structure contacting the solder bumps results in the inability to effectively draw heat from the solder bumps 22 or localized hot points. Thus, heat dissipating through the solder bumps 22 will cause thermal fatigue in the solder bump interconnections between the die 10 and substrate 12.
Therefore, it would be advantageous to provide a method and apparatus that transfer heat from a flip-chip assembly that limits the potential thermal fatigue to the semiconductor assembly.
The present invention relates to a method and apparatus for transferring heat from a flip-chip semiconductor device assembly to help limit and control any thermal fatigue of the flip-chip semiconductor device assembly. The present invention is directed to a method and apparatus for providing a heat sink that dissipates heat away from the semiconductor die of the assembly. The present invention includes a diamond layer overlying a surface of a semiconductor die for channeling heat from the semiconductor die in a semiconductor device assembly.
In one embodiment, the present invention includes a diamond layer deposited or formed on the active surface of a semiconductor die, the diamond layer having at least one opening therein. At least one bond pad formed on the active surface of the semiconductor die extends partially through the at least one opening in the diamond layer. According to the present invention, the diamond layer thermally conducts heat from the at least one bond pad of the semiconductor die being partially in contact therewith. Further, the diamond layer dissipates the heat away from the semiconductor die.
In another embodiment, the present invention includes a diamond layer having at least one opening or via therein deposited or formed over a surface, typically the active surface, of a semiconductor die. The diamond layer includes a trace formed therein for electrical communication between the semiconductor die and a contact pad formed in the opening or via in the diamond layer. In this embodiment, the diamond layer thermally conducts heat from the substrate, the trace and the contact pad. In turn, the heat dissipates from the diamond layer.
In another embodiment, the present invention includes a semiconductor die having a surface, typically the active surface, with a first diamond layer, or film, deposited or formed thereon. Bond pads of the semiconductor die are exposed through the first diamond layer. A second diamond layer is formed over the first diamond layer having a passivation layer therebetween. A conductive trace is formed in the passivation layer to electrically communicate with the semiconductor die and a conductive pad provided in openings in the second diamond layer. According to the present invention, the conductive pad extends partially over and in contact with the second diamond layer to thermally conduct heat therefrom and, in addition, the first diamond layer directly contacts the active surface of the semiconductor die to thermally conduct heat therefrom. As a result, the present invention provides a method and apparatus for thermally conducting heat from a semiconductor device to prevent thermal fatigue in the interconnections therein.